A significant number of cell towers in the US are not what they seem to be. In fact, at least according to a recent report, it’s likely they are snooping on your calls.
One of the impressive things about GSM is that despite being a standard that was devised nearly a quarter of a century ago, it’s still pretty secure. If you're looking to listen into calls, it’s actually much easier to just switch off the encryption. Les Goldsmith, the CEO of ESD America, which sells a security-hardened phone, says he has found a number of cell sites which do exactly this.
Goldsmith told the US publication Popular Science that he knew of 17 mobile phone towers which forced his phone to 2G and then switched off the encryption. He dubs these as “interceptors” on the basis that they might be running man-in-the-middle attacks where the rogue tower takes a call, siphons it off for interception and also passes it on to the legitimate network.
One (American) expert who works in the field told El Reg: “The Americans can be very melodramatic about things. It is highly unlikely that this 'interceptor' stuff will become common in the UK due to licensing and call charges.
"It is most probable that these sites are to allow coverage to groups of people that are not in a conventional coverage area (such as paying customers in a casino, or military groups). I would suggest that university campus areas may do the same. It does allow "man in the middle" attacks to be carried out on standard users if that were the purpose of the towers... which I doubt!”
Another very senior expert told us: “False base stations are always possible on GSM. It does not surprise me. Of course, encryption can be turned off by the operator, or by the State such as China or India. It does not happen on 3G or LTE if you are using mutual authentication.”
In the past, network planners have told us about interesting anomalies in coverage around some London embassies.
It’s also worth noting that many phones – even feature phones – will notify you if they are connected to a network without encryption. And in some cases this might be because the country you are in cannot get the export licences necessary to install encrypted infrastructure. ®